In recent years, much attention has been given to a vehicle, as an environmentally-friendly vehicle, equipped with a power storage device (for example, a secondary battery, a capacitor and the like) and running with the driving force generated from the electric power stored in the power storage device. Such a vehicle includes, for example, an electric vehicle, a hybrid vehicle, a fuel cell vehicle, and the like.
It is known that some hybrid vehicles have a power storage device mounted on the vehicle and chargeable from an electric power supply external to the vehicle, like the electric vehicles. For example, a so-called “plug-in hybrid vehicle” is known that has a power storage device chargeable from a power supply of an ordinary household by connecting a power supply outlet provided at the house and a charging inlet provided at the vehicle by means of a charging cable.
As for the way to transmit electric power, wireless power transmission without using a power supply cord and a power transmission cable has been of interest in recent years. Three techniques are known as predominant wireless power transmission techniques, namely power transmission by means of electromagnetic induction, power transmission by means of electromagnetic wave and power transmission by means of a resonance method.
Among these techniques, the resonance method is a contactless power transmission technique according to which a pair of resonators (a pair of self-resonant coils, for example) is caused to resonate in an electromagnetic field (near field) and electric power is transmitted through the electromagnetic field. With the resonance method, a large amount of electric power of a few kW can be transmitted over a relatively long distance (a few meters, for example).
Japanese Patent Laying-Open No. 2009-106136 (PTL 1) discloses a technique of receiving charging power wirelessly from a power supply external to the vehicle by the resonance method, and allowing charging of a vehicle-mounted power storage device.
Japanese Patent Laying-Open No. 2004-356765 (PTL 2) discloses a technique by a contactless data carrier including a coil-shaped antenna and a variable capacitor for adjusting a resonance frequency with a contactless reader writer to perform wireless communication.